The present invention relates generally to fabrics, and more particularly to electric heating fabrics such as electric blankets.
In general, an electric blanket, a warming blanket, or an electric heating blanket, is a blanket containing an insulated electric heating element. An electric blanket is typically plugged into a power outlet so that power may be supplied to the heating element, causing the production of heat. In this manner, the electric blanket may be a warm, comfortable cover, or may be used to warm a bed, for example.
Contemporary electric blankets usually include controls that permit a user to set the amount of heat output of the blanket. This feature allows the consumer to set the blanket to a setting that offers the desired amount of heat for a particular temperature and in accordance with the comfort level of the individual.
Although present electric blankets work well for their intended purpose, often they are uncomfortable for a user when there are temperature changes after the controls for the blanket have been set. For example, a user may utilize an electronic thermostat for the home that is programmable to cause the temperature of the house to decrease during the night, and to increase the temperature of the house just prior to a wakening time. Such temperature changes may not be taken into account by the manufacturer of the electric blanket, and a heat output setting that was comfortable when the electric blanket was set (e.g., when the room was 70 degrees) may not be comfortable when the room temperature decreases during the night (e.g., drops to 60 degrees). As such, the user may feel cold during the night when the temperature drops to the lower temperature. The user may reset the blanket to a higher setting, but changing the setting may require waking up during the night, finding the controls for the electric blanket, and setting the controls to the new setting. Moreover, the new, higher setting may be uncomfortably warm when the room temperature returns to a higher setting (e.g., 70 degrees) in the morning.
The present invention provides a warming fabric having temperature compensation controls that vary the heat output of the warming fabric to adjust for changes in ambient temperature. To this end, the present invention utilizes a thermistor or another mechanism that is configured to generate information about the temperature of the location of the fabric (temperature data mechanism). In the case of the thermistor, because resistance varies with temperature of the thermistor, fixed current applied to the thermistor will vary the voltage reading across the thermistor with changes in temperature. This information may be used to generate temperature data. For example, a thermistor and a fixed series resistor may be connected in series to a fixed voltage, and the voltage at the junction of the thermistor and the series resistor may be measured and supplied to a microcomputer. Because the thermistor""s resistance varies with temperature, the voltage at the junction varies with the temperature changes.
In accordance with one aspect of the present invention, the relationship between the temperature and the output of the temperature data mechanism is approximately linear over the typical operating temperature range where most blankets are used (e.g., 50 to 80 degrees Fahrenheit). In the case of the thermistor described above, the approximately linear information is the voltage at the juncture of the two resistors. This juncture is connected to a microcomputer that programmed to set the heat output of the warming fabric. An A/D converter converts the analog voltage reading at the juncture into a digital value. The microcomputer may then use the digital value to determine how the fabric heat output should be modified due to the ambient temperature. To do so, a look up table or an algorithm may be used to calculate the appropriate heat output.
The combination of the fixed resistor and the thermistor require very little additional PC board area and may be added to existing controls with little effort or cost. As such, the present invention provides a relatively inexpensive warming fabric control that may easily adjust for varying ambient temperature conditions.